This application addresses broad Challenge Area CLINICAL RESEARCH and specific Challenge Topic, 04-DK-103: Develop Novel Approaches to Understand and Treat Functional Disorders. In this application, we plan to determine the role of diet in the development of functional GI and motility disorders and how genotype contributes to the development of functional GI and motility disorders. The genotype of interest is the mixed histocompatibility complex, HLA. There is epidemiological evidence of significant overlap between irritable bowel syndrome (IBS) and functional chronic diarrhea [FD (Locke et al 2005)]. The relationship of celiac disease and IBS is complex;while guidelines suggest screening for celiac disease in patients with FD or IBS with diarrhea (IBS-D), there is a paucity of evidence to support that recommendation. In Olmsted Co., MN, overall prevalence of positive tissue transglutaminase serology was 4%, and celiac disease did not explain the presence of either IBS or dyspepsia (Locke et al 2004). In a cost effectiveness analysis, testing for celiac disease became the dominant strategy when prevalence was >8%, specificity of the test for celiac disease was >98%, or the cost of IBS treatment exceeded $130/month (Spiegel BM, et al 2004). In fact, the incremental cost of testing for celiac disease exceeded $50,000 when the prevalence fell below 1%. Community studies suggest that celiac disease affects 0.5 to 1.0% of people in the USA. On the other hand, there is increasing recognition of a potential role of intolerance to gluten in patients with IBS-D or FD. Gluten intolerance without celiac disease was first popularized as a clinical entity in 1981 (Cooper BT et al 1981). However, until recently, there have been very limited investigations of the role of gluten intolerance as a factor contributing to IBS-D or FD. Wahnschaffe et al demonstrated that, among patients with IBS-D or FD, response of diarrhea to GFD was influenced by the HLA type and the presence of IgG tissue transglutaminase antibody: for HLA DQ 2 +ve, IgG TGA +ve, the response to gluten withdrawal occurred in 62%;conversely, in those DQ 2 -ve and IgG TGA -ve, 12% responded (Wahnschaffe et al 2007). This suggests that there is an immunogenetic predisposition to gluten intolerance among patients with IBS-D or FD in the absence of celiac disease. The mechanisms underlying this intolerance of gluten in humans with IBS are unclear. In HLA-D8 transgenic mice sensitized to gluten, gliadin exposure (in contrast to negative and positive controls) results in CD3, CD4 lymphocyte and macrophage infiltration of villi, and increased contractile responses of smooth muscle to electrical field stimulation and carbachol (Verdu et al 2008). This contractile activity may be a mechanism for the development of diarrhea. The link between gluten or gliadin and inflammation may be the increase in intestinal permeability, which is well established in celiac disease and involves binding to the chemokine receptor, CXCR3, leading to MyD88-dependent zonulin release (Lammers et al 2008). It is still unclear whether gluten alters permeability in the absence of celiac disease. On the other hand, there are reports of increased mucosal permeability in IBS, both non-infectious and post-infectious varieties, that typically causes IBS-D (Dunlop et al 2006). Our overall hypothesis is that gluten intake increases intestinal permeability in susceptible patients and leads to alterations in gastrointestinal function that manifest as IBS-D or chronic diarrhea. Our overall aim is to understand the mechanism of gluten-induced symptoms in patients with symptoms suggestive of IBS-D or FD, and optimize treatment of these patients. We propose to test the following: Specific hypotheses: 1. IBS-D or FD patients who are HLA-DQ2 positive have higher small intestinal and colonic permeability than HLA-DQ2 negative patients. 2. Gluten supplementation for four weeks increases small intestinal permeability and accelerates colonic transit in patients with IBS-D or FD who are HLA-DQ2 positive. Specific aims: 1. To compare small intestinal and colonic permeability in patients with IBS-D or FD who are positive or negative for HLA-DQ2. 2. To compare in a parallel-group, randomized, controlled trial, the effect of gluten-rich versus gluten-free diet on small intestinal and colonic permeability, small bowel and colonic mucosal morphology, and gastrointestinal and colonic transit in HLA-DQ2 positive and HLA-DQ2 negative patients with IBS-D or FD. PUBLIC HEALTH RELEVANCE: This application addresses the Challenge Area of Clinical Research in Digestive Diseases and the development of novel approaches to understand and treat functional GI and motility disorders. The application focuses specifically on the role of gluten (a protein in flour) diet and patients'genetic make-up in the development of chronic diarrhea and irritable bowel syndrome (IBS) with diarrhea, and how gluten free diet normalizes intestinal functions and bowel movements.